1. Field of the Invention
The present invention relates to a circuit and method for controlling a cursor on a video display terminal.
2. Description of the Prior Art
A conventional mouse, track ball, joy stick, touch sensitive pad, pressure sensitive pad, or virtual reality position sensor (hereinafter jointly referred to as peripheral computer input devices) can be used to position a cursor on a computer screen. Peripheral computer input devices typically include a button which can be actuated by a user to perform additional functions, such as operating pull-down or pop-up menus, sizing windows and making selections.
Conventional peripheral computer input devices have one or more disadvantages. First, they require a certain amount of physical space in which to operate. When operating a computer in a small operating space (e.g., on an airplane, in a bus), conventional peripheral computer input devices become cumbersome or impossible to use in such environments.
Additionally, peripheral computer input devices are somewhat inconvenient because their operation requires the user to completely remove at least one hand from the area of the keyboard. Moreover, conventional peripheral computer input devices require moving mechanical parts which can experience mechanical wear over extended periods of use. These mechanical parts are relatively expensive to manufacture and replace. Furthermore, conventional computer input devices are cumbersome because they typically require a wire to be connected between the input device and the computer.
Some peripheral computer input devices have been integrated into portable computers. However, there are disadvantages to such integrated computer input devices. For example, the integrated computer input device consumes valuable space within the portable computer. In addition, the integrated computer input device is typically placed in an inconvenient location on the portable computer due to size constraints. Furthermore, the miniaturization which allows the computer input device to be integrated with the computer results in diminished usability of the computer input device. No integrated portable computer input device has yet matched the usability of a conventional desktop mouse.
Several alternatives have been developed which attempt to remedy the above listed shortcomings of conventional peripheral computer input devices. However, none of these alternatives have completely addressed the above-listed problems. Certain of these alternatives are described in U.S. Pat. Nos. 4,954,817 (Levine); 4,988,981 (Zimmerman et al.); 3,846,580 (Brenner); 3,904,821 (Whetstone et al.); 4,540,176 (Baer); 4,927,987 (Kirchgessner); 5,095,302 (McLean et al.); and 5,010,500 (Makkuni et al.).
It would therefore be desirable to have a computer input device which overcomes the above-listed disadvantages of conventional peripheral computer input devices.